The invention concerns contact connections of sound reproduction devices which operate in accordance with the flexural wave principle.
Sound reproduction devices containing conical, flat or spherical diaphragms which are widely used to reproduce sound events, have stranded conductors that are optimized to provide an electrical contact between a stationary terminal block and the voice coil which is connected to the respective diaphragm. The special design of the conductors ensures that a permanent contact is achieved, which barely hinders the movement of the voice coil in spite of the relative movement between the voice coil and the stationary terminal block.
In addition to such sound reproduction devices, those operating in accordance with the flexural wave principle have become known of late. Such devices are essentially composed of a panel and at least one drive system, where the panel is made to oscillate when low frequency sound signals are conducted to the drive system or systems. It is characteristic for such sound reproduction devices that a flexural wave radiation is enabled starting from a critical lower cut-off frequency, where the flexural waves create a sound radiation in a frequency-dependent direction along the plane of the respective panel. In other words, a cut through a directivity diagram shows a principal lobe whose direction is frequency-dependent.
The panel is constructed in accordance with the sandwich principle, where two opposite surfaces of a very light core layer are respectively attached to a thin cover layer, for example by means of an adhesive. For the panel to have good sound reproduction properties, the material for the cover layer must have an especially high dilatational wave speed. Suitable cover layer materials are for example thin metal foils and also fiber-reinforced plastic foils. Special demands are also made on the core layer since this layer must have a very high modulus of elasticity in the direction of the two surfaces that are equipped with cover foils, while it must have a very low modulus of elasticity in the direction that is parallel to the surfaces equipped with cover foils. This anisotropic behavior of the core layer is achieved for example by giving the core layer a honeycomb structure in which the walls that form the honeycombs extend vertically to the two cover layers. Light metals and fiber-reinforced plastics proved to be suitable materials for the honeycomb structure of the core layer. It is also possible to use hard foams for the core layer insofar as they have openings that extend between the two cover layers.
If sound reproduction devices according to the flexural wave principle are equipped with drive systems which are integrated into or onto the panel as illustrated in a parallel application, the electrical connections known from sound reproduction devices with conical, flat or spherical diaphragms cannot be used to make contact with the voice coil. This can be attributed to the fact that high current intensities must be supplied to the drive systems of sound reproduction devices that operate in accordance with the flexural wave principle. Because of the high accelerating forces, this can only be realized with very stable contact connections, which however heavily dampen the flexural wave propagation.
It is therefore the object of the invention to propose a contact connection for sound reproduction devices according to the flexural wave principle, which is very simple to implement and has a heavily reduced damping effect on the flexural wave propagation and avoids voltage losses due to high transition resistances.
This object is achieved by a contact connection for a sound reproduction device according to the flexural wave principle, with a panel which is composed of a core layer, a top and a bottom cover layer, where the two cover layers are attached to opposite sides of the core layer, and with at least one drive system which is connected to the panel and can be connected to a sound signal source by means of two lines, wherein at least one of the two cover layers and/or the core layer have conductive areas, and that these conductive areas are conductively connected to the lines of the sound signal source and the corresponding connections of the respective drive systems.
The basic idea of the invention is to use the components of the panel for contacting the voice coil and the sound signal source, because it has been discovered that the cover layers and/or the core layer can be used as exceptionally good power conductors for the voice coil if the core layer or at least one of the cover layers contain conductive areas.
The two cover layers which cover the core layer can be used as conductive areas if they are manufactured of a material that conducts electric current and are separated by an insulating core layer. The use of two cover layers which are entirely manufactured of a conductive material also has the additional advantage that when using a number of drive systems per panel, no separate power conductors need to be supplied for the individual drive systems. The electrical connection of the respective drive system only requires that the respective contacts of this drive system are connected to one of the two cover layers. This type of contact connection of drive systems achieves a high flexibility in the arrangement of the drive systems in or on the panel, because any changes in the arrangement of the different drive systems do not require any reconfiguration of the power supply.
Only one cover layer of conductive material is necessary if the cover layer is subdivided into at least two insulated segments. Such an arrangement has the advantage that the panel requires no special insulation if the cover layer which is subdivided into segments is located so that it faces away from the listening room.
The core layer can also be used as a power conductor if it contains conductive areas.
If it is necessary to construct the conductive areas of the core layer massively, they must then have the same distance from the cover layers. This ensures that these conductive areas are not subjected to stretch forces from the effect of flexural waves.
If the core layer has a perforated structure that contains openings, and if the core layer is formed of an insulator, these openings can also be very simply used to conduct signals if the openings are equipped with a conductor which is connected to the corresponding conductive area. Such conductors are not limited to the conductive plastic materials that fill the respective openings, but they can also be massive wires since conducting the wires in the openings does not hinder the bending of the core layer 11 crosswise to its greatest expansion.
If the core layer is formed of a number of small strips, where each strip which is adjacent to another strip is connected to it by a number of reciprocally separated connection places extending in the direction of the narrow side of the strips, and where the unconnected areas of the strips are placed at a reciprocal distance from each other, and if at least one of these strips is made of a conductive material, it is possible to produce conductive areas in the core layer without any special effort.
The above-mentioned openings can be used to transmit the sound signal conducted in the strip or strips, if these openings are equipped with a conductor which is connected to said conductive material strip.
The supply of sound signals to the panel is particularly simple if the panel is surrounded by a holder and is connected thereto. It is particularly advantageous if the attachment means whereby the panel is linked to the holder simultaneously establish a conductive connection between the stationary connection clamps on the holder and the corresponding conductive area of cover layer and/or core layer.